1. Field of the Invention
In one of its aspects, the present invention relates to a fluid treatment system, more particularly, an ultraviolet radiation water treatment system. In another of its aspects, the present invention relates to a method for treating a fluid, more particularly a method for irradiating water.
2. Description of the Prior Art
Fluid treatment systems are generally known in the art. More particularly, ultraviolet (UV) radiation fluid treatment systems are generally known in the art. Early treatment systems comprised a fully enclosed chamber design containing one or more radiation (preferably UV) lamps. Certain problems existed with these earlier designs. These problems were manifested particularly when applied to large open flow treatment systems which are typical of larger scale municipal waste water or potable water treatment plants. Thus, these types of reactors had associated with them the following problems:
relatively high capital cost of reactor;
difficult accessibility to submerged reactor and/or wetted equipment (lamps, sleeve cleaners, etc);
difficulties associated with removal of fouling materials from fluid treatment equipment;
relatively low fluid disinfection efficiency, and/or
full redundancy of equipment was required for maintenance of wetted components (sleeves, lamps and the like).
The shortcomings in conventional closed reactors led to the development of the so-called “open channel” reactors.
For example, U.S. Pat. Nos. 4,482,809, 4,872,980 and 5,006,244 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #1 Patents) all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Such systems include an array of UV lamp modules (e.g., frames) which include several UV lamps each of which are mounted within sleeves which extend between and are supported by a pair of legs which are attached to a cross-piece. The so-supported sleeves (containing the UV lamps) are immersed into a fluid to be treated which is then irradiated as required. The amount of radiation to which the fluid is exposed is determined by the proximity of the fluid to the lamps, the output wattage of the lamps and the flow rate of the fluid past the lamps. Typically, one or more UV sensors may be employed to monitor the UV output of the lamps and the fluid level is typically controlled, to some extent, downstream of the treatment device by means of level gates or the like.
The Maarschalkerweerd #1 Patents teach fluid treatment systems which were characterized by improved ability to extract the equipment from a wetted or submerged state without the need for full equipment redundancy. These designs compartmentalized the lamp arrays into rows and/or columns and were characterized by having the top of the reactor open to provide free-surface flow of fluid in a “top open” channel.
The fluid treatment system taught in the Maarschalkerweerd #1 Patents is characterized by having a free-surface flow of fluid (typically the top fluid surface was not purposely controlled or constrained). Thus, the systems would typically follow the behavior of open channel hydraulics. Since the design of the system inherently comprised a free-surface flow of fluid, there were constraints on the maximum flow each lamp or lamp array could handle before either one or other hydraulically adjoined arrays would be adversely affected by changes in water elevation. At higher flows or significant changes in the flow, the unrestrained or free-surface flow of fluid would be allowed to change the treatment volume and cross-sectional shape of the fluid flow, thereby rendering the reactor relatively ineffective. Provided that the power to each lamp in the array was relatively low, the subsequent fluid flow per lamp would be relatively low. The concept of a fully open channel fluid treatment system would suffice in these lower lamp power and subsequently lower hydraulically loaded treatment systems. The problem here was that, with less powerful lamps, a relatively large number of lamps was required to treat the same volume of fluid flow. Thus, the inherent cost of the system would be unduly large and/or not competitive with the additional features of automatic lamp sleeve cleaning and large fluid volume treatment systems.
This led to the so-called “semi-enclosed” fluid treatment systems.
U.S. Pat. Nos. 5,418,370, 5,539,210 and Re 36,896 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #2 Patents) all describe an improved radiation source module for use in gravity fed fluid treatment systems which employ UV radiation. Generally, the improved radiation source module comprises a radiation source assembly (typically comprising a radiation source and a protective (e.g., quartz) sleeve) sealingly cantilevered from a support member. The support member may further comprise appropriate means to secure the radiation source module in the gravity fed fluid treatment system.
Thus, in order to address the problem of having a large number of lamps and the incremental high cost of cleaning associated with each lamp, higher output lamps were applied for UV fluid treatment. The result was that the number of lamps and subsequent length of each lamp was dramatically reduced. This led to commercial affordability of automatic lamp sleeve cleaning equipment, reduced space requirements for the treatment system and other benefits. In order to use the more powerful lamps (e.g. medium pressure UV lamps), the hydraulic loading per lamp during use of the system would be increased to an extent that the treatment volume/cross-sectional area of the fluid in the reactor would significantly change if the reactor surface was not confined on all surfaces, and hence such a system would be rendered relatively ineffective. Thus, the Maarschalkerweerd #2 Patents are characterized by having a closed surface confining the fluid being treated in the treatment area of the reactor. This closed treatment system had open ends which, in effect, were disposed in an open channel. The submerged or wetted equipment (UV lamps, cleaners and the like) could be extracted using pivoted hinges, sliders and various other devices allowing removal of equipment from the semi-enclosed reactor to the free surfaces.
The fluid treatment system described in the Maarschalkerweerd #2 Patents was typically characterized by relatively short length lamps which were cantilevered to a substantially vertical support arm (i.e., the lamps were supported at one end only). This allowed for pivoting or other extraction of the lamp from the semi-enclosed reactor. These significantly shorter and more powerful lamps inherently are characterized by being less efficient in converting electrical energy to UV energy. The cost associated with the equipment necessary to physically access and support these lamps was significant.
Historically, the fluid treatment modules and systems described in the Maarschalkerweerd #1 and #2 Patents have found widespread application in the field of municipal waste water treatment (i.e., treatment of water that is discharged to a river, pond, lake or other such receiving stream).
In the field of municipal drinking water, it is known to utilize so-called “closed” fluid treatment systems or “pressurized” fluid treatment systems.
Closed fluid treatment devices are known—see, for example, U.S. Pat. No. 5,504,335 (Maarschalkerweerd #3). Maarschalkerweerd #3 teaches a closed fluid treatment device comprising a housing for receiving a flow of fluid. The housing comprises a fluid inlet, a fluid outlet, a fluid treatment zone disposed between the fluid inlet and the fluid outlet, and at least one radiation source module disposed in the fluid treatment zone. The fluid inlet, the fluid outlet and the fluid treatment zone are in a collinear relationship with respect to one another. The at least one radiation source module comprises a radiation source sealably connected to a leg which is sealably mounted to the housing. The radiation source is disposed substantially parallel to the flow of fluid. The radiation source module is removable through an aperture provided in the housing intermediate to fluid inlet and the fluid outlet thereby obviating the need to physically remove the device for service of the radiation source.
U.S. Pat. No. 6,500,346 [Taghipour et al. (Taghipour)] also teaches a closed fluid treatment device, particularly useful for ultraviolet radiation treatment of fluids such as water. The device comprises a housing for receiving a flow of fluid. The housing has a fluid inlet, a fluid outlet, a fluid treatment zone disposed between the fluid inlet and the fluid outlet and at least one radiation source having a longitudinal axis disposed in the fluid treatment zone substantially transverse to a direction of the flow of fluid through the housing. The fluid inlet, the fluid outlet and the fluid treatment zone are arranged substantially collinearly with respect to one another. The fluid inlet has a first opening having: (i) a cross-sectional area less than a cross-sectional area of the fluid treatment zone, and (ii) a largest diameter substantially parallel to the longitudinal axis of the at least one radiation source assembly.
Practical implementation of known fluid treatment systems of the type described above have been such that the longitudinal axis of the radiation source is: (i) parallel to the direction of fluid flow through the fluid treatment system, or (ii) orthogonal to the direction of fluid flow through the fluid treatment system. Further, in arrangement (ii), it has been common to place the lamps in an array such that, from an upstream end to a downstream end of the fluid treatment system, a downstream radiation source is placed directly behind an upstream radiation source.
The use of arrangement (ii) in an UV radiation water treatment system has been based on the theory that radiation was effective up to a prescribed distance from the radiation source, depending on the transmittance of the water being treated. Thus, it has become commonplace to interspace the radiation sources in arrangement (ii) such that the longitudinal axes of adjacent radiation sources are spaced at a distance equal to approximately twice the prescribed distance mentioned in the previous sentence.
Unfortunately, for the treatment of large volumes of fluid, arrangement (ii) can be disadvantageous for a number of reasons. Specifically, implementation of arrangement (ii) requires a relatively large “footprint” or space to house the radiation sources. Further, the use of a large number of radiation sources in arrangement (ii) creates a relatively large coefficient of drag resulting in a relatively large hydraulic pressure loss/gradient over the length of the fluid treatment system. Still further, the use of a large number of radiation sources in arrangement (ii) can produce vortex effects (these effects are discussed in more detail hereinbelow) resulting in forced oscillation of the radiation sources—such forced oscillation increases the likelihood of breakage of the radiation source and/or protective sleeve (if present).
Accordingly, there remains a need in the art for a fluid treatment system, particularly a closed fluid treatment system which has one or more of the following features:
it can treat large volumes of fluid (e.g., wastewater or drinking water and the like);
it can increase the limit of the maximum admissible velocity through the reactor;
it requires a relatively small “footprint”;
it results in a relatively lower coefficient of drag resulting in an improved hydraulic pressure loss/gradient over the length of the fluid treatment system;
it results in relatively lower (or no) forced oscillation of the radiation sources thereby obviating or mitigating breakage of the radiation source and/or protective sleeve (if present);
it can be readily adapted to make use of relatively recently developed so-called “low pressure high output” (LPHO), amalgam and/or other UV emitting lamps while allowing for ready extraction of the lamps from the fluid treatment system for servicing and the like;
it can employ a lamp of a standard length for varying widths of reactors;
it can be readily combined with a cleaning system for removing fouling materials from the exterior of the radiation source(s);
it can be readily installed in a retrofit manner in an existing fluid treatment plant; and
it provides relatively improved disinfection performance compared to conventional fluid treatment systems.